This project advances the development of a mechanical auxiliary ventricle (MAV) for the treatment of intractable chronic left ventricular failure. The long-term objective is to qualify the MAV system for FDA approval for clinical investigation and to make it commercially available. The system's components are an avalvular pumping chamber implanted in the descending thoracic aorta, an external pneumatic power source, and a percutaneous access device (PAD). Clinical trial of an earlier version of the MAV in 3 patients confirmed substantial hemodynamic efficacy for periods up to 96 days, but showed the PAD to be failure-prone. In later laboratory studies it was found that the blood pump's constituent layers could harbor cellular debris, forming a nidus of infection. Since then, research and development of a new PAD have resulted in promise of a stable device; and a new single-layer improved design of the pumping chamber has also been evolved. The objective of Phase I studies is to confirm that the redesigned pumping chamber is ready for long-term in-vivo evaluation. The MAV implanted in 5 calves, will be pumped on a 6 hour ON, 6 hour OFF schedule for six weeks. This will provide a test of the adequacy of the aortic suture line. Throughout the study, clotting parameters will be screened. The animals will then be sacrificed so that the MAV and adjacent tissues can be examined and a careful search for emboli made. These studies are prerequisite to Phase II efforts.